Publications

4721

Abstract‘Candidatus Phytoplasma (Ca. P.) solani’ is associated with Bois noir (BN) of grapevine and stolbur of solanaceous plants and is primarily transmitted by Hyalesthes obsoletus Signoret. Four tuf‐a and five tuf‐b1 ‘Ca. P. solani’ strains were transmitted to tomato plants (cv. Micro‐Tom) to set the basis for studying molecular interactions between different strains of the pathogen and host plants. The strains were acquired by using bait‐plants and by capturing H. obsoletus adults on bindweed and stinging nettle in vineyards of Friuli Venezia Giulia (northeastern Italy) with a high prevalence of BN. Captured insects were forced to feed on healthy tomato plants to induce infection. All strains obtained from symptomatic plants and confirmed by real‐time PCR were maintained on tomato through grafting. Successively, the strains were characterised by macroscopic and microscopic symptoms induced in the host, Multi‐Locus Sequence Typing (MLST) based on tuf, secY, stamp, and vmp1 genes, in‐planta spread and multiplication patterns. Molecular typing distinguished the strains into five lineages comprised in three clusters: one including strains of tuf‐a genotype and two including strains of tuf‐b1 genotype. Quite different symptoms were induced on tomatoes by strains belonging to the two tuf genotypes; infection by tuf‐a strains resulted in plant decline around 95–100 days after grafting and absence of cauliflower‐like inflorescence with symptoms of phyllody and virescence, which were usually associated with tuf‐b1 strains. The different symptoms, the outcome of disease, and the ultrastructural observation performed on sieve elements suggested a higher virulence of tuf‐a strains in tomato. Overall, our results propose that genomic variability of ‘Ca. P. solani’ strains should be extensively explored to determine possible associations with type of symptoms and strain virulence.

ABSTRACT Huanglongbing (HLB), caused by Candidatus Liberibacter asiaticus (CLas), is the most devastating citrus disease worldwide. Developing effective therapies remains a major challenge, as CLas cannot be cultured in vitro and colonizes the host phloem systemically. This study presents a rapid, reproducible, and cost-effective in vivo platform for screening bacteriostatic and bactericidal compounds using CLas-infected citron (Citrus medica (L.) Osbeck) stem cuttings. Among seven citrus genotypes tested, citron stem cuttings exhibited superior rooting performance and uniform vegetative growth. Four propagation protocols were developed and assessed based on the dynamics of rooting and shoot growth, CLas colonization, and the response to oxytetracycline (OTC) treatment. CLas+ stem cuttings were treated with OTC via drenching at different developmental root stages. The roots or new vegetative flushes were sampled for bacterial quantification by qPCR. In Protocol 2, in which treatments were applied and sampled 14 and 35 days after planting (DAP) respectively, OTC-treated roots achieved the highest suppression of CLas and the lower incidence of CLas+ rooted cuttings compared to non-treated roots. Time-course analysis showed that OTC delayed bacterial establishment in root tissues, with maximal suppression observed at 35 DAP. The proposed protocols simulate the natural progression of systemic infection in citrus plants, allow the assessment of phytotoxicity, and offer a scalable technology that does not underestimate the efficacy of future bactericidal candidates. This platform significantly reduces time and cost compared to traditional seedling or nursery tree experiments and enhances the early-phase screening of antimicrobial compounds. Altogether, this stem cutting-based approach represents a biologically relevant, scalable tool to accelerate therapeutic discovery and strengthen integrated HLB management strategies.

Abstract Numerous cyanobacterial strains previously identified as Scytonema hyalinum were determined to be phylogenetically distant from the type species of Scytonema, S. hofmannii . Morphological and molecular evidence suggests this distinct clade necessitates placement in a new genus, and we have described Kalymmatonema gen. nov. herein. Kalymmatonema has been demonstrated to exhibit five ribosomal operons, all of which differed in both sequence and secondary structure of conserved helical domains in the 16S–23S internal transcribed spacer rRNA region. Four of these operon copies were highly similar in 16S and 23S rRNA gene sequences, whereas the divergent fifth copy is thought to represent a whole‐operon horizontal gene transfer event. Through in‐depth analysis, we were able to recognize seven species new to science, the type species K. desertorum sp. nov., K. arcangelii comb. nov., K. chimaera sp. nov., K. ethiopiense sp. nov., K. gypsitolerans sp. nov., K. mateoae sp. nov., and K. oahuense sp. nov. We also created the new combination, K. hyalinum comb. nov., in order to include the original Scytonema hyalinum in this new genus based upon the common morphological feature of a mucilaginous apical cap on the trichomes. Kalymmatonema displays a complex evolution of its ribosomal operons, with evidence not only of horizontal gene transfer but also of internal rearrangements and mobile genetic elements that have transposed the tRNA‐containing region of the ITS rRNA region among the four similar operons. Additional investigation of the evolutionary history of this interesting genus will likely lead to a better understanding of the processes shaping ribosomal evolution in cyanobacteria.

ABSTRACT Insects of the suborder Auchenorrhyncha harbour multiple ancient endosymbionts that jointly produce essential nutrients lacking from the host's diet. Compared to cicadas, leafhoppers, and spittlebugs, our understanding of the multipartite symbioses among planthoppers, an extremely diverse insect group, is still very limited. Herein, we assembled the genomes of the primary endosymbionts of two planthopper species from the Cixiidae family, Cixius wagneri and Pentastiridius leporinus , both vectors of phytopathogenic Arsenophonus in Europe. Each species harboured a different tripartite endosymbiont consortium: while P. leporinus carried the well‐known combination ‘ Candidatus Karelsulcia muelleri’, ‘ Ca . Vidania fulgoroideae’, and ‘ Ca . Purcelliella pentastirinorum’, C. wagneri harboured a yet unknown Gammaproteobacterium in addition to Karelsulcia and Vidania . This new endosymbiont ‘ Ca . Mirabilia symbiotica’ is likely much older than Purcelliella , considering its extremely reduced genome. In both species, Karelsulcia and Vidania jointly produce the 10 essential amino acids, whereas Purcelliella and Mirabilia provide the non‐essential amino acid cysteine and slightly different gene sets encoding B vitamins. Our findings confirm the functional stability of multipartite planthopper endosymbiont consortia despite changing partners over evolutionary time. In addition, we describe a new Rickettsia strain from the Meloidae group colonising P. leporinus , highlighting the diversity of bacterial endosymbionts associated with planthoppers.

Abstract Background Candidatus Phytoplasma infection is among the most destructive plant diseases, characterized by phyllody, witches broom, virescence etc. Sesame (Sesamum indicum L.), one of the oldest cultivated oilseed crops, valued for its nutritional and medicinal properties, is highly susceptible to phytoplasma infection, causing substantial annual yield losses. The present study aimed to investigate the metabolomic and molecular alterations in sesame plants as a consequence of phytoplasma infection in two distinct tissue types, leaves and flowers, using a multi-omics approach. Results The study revealed that phytoplasma infection significantly alters the expression of floral homeobox and meristem identity genes in an antagonistic manner, resulting in the development of leaf-like traits in floral tissues. Integrated analyses of transcriptomic and metabolomic datasets showed that control leaves, control flowers, infected leaves, and infected flowers each displayed distinct metabolomic and transcriptomic profiles. Metabolomic profiling demonstrated major changes in pathways such as porphyrin metabolism, brassinosteroid metabolism, and phenylpropanoid biosynthesis. Complementary KEGG pathway enrichment analysis of transcriptome data confirmed strong enrichment of secondary metabolite biosynthesis in both tissue types upon infection. Tissue-specific responses were evident. Floral tissues accumulated green pigments due to increased porphyrin biosynthesis and reduced degradation, while leaves showed simultaneous upregulation of both biosynthesis and breakdown pathways of porphyrins. Floral tissues exhibited stronger stress-associated responses, including upregulation of genes related to stress enzymes, phenylpropanoids, and lignification-related metabolites. In contrast, certain compounds such as lignans were specifically accumulated in leaves upon infection. These observations were further supported by biochemical, histological, and qRT-PCR assays. Conclusion This study provides the first clear evidence of tissue-specific metabolic reprogramming in sesame under Ca. Phytoplasma infection through integrated transcriptomic and metabolomic analyses. These findings improve our understanding of host-pathogen interactions and offer a basis for strategies to reduce phytoplasma-induced yield losses.

AbstractBACKGROUNDAutophagy is a conserved mechanism by which eukaryotic organisms defend against pathogen infection. However, the molecular mechanisms underlying the role of autophagy in the interactions of insect vectors with the phloem‐limited bacterial pathogen remain unclear. The citrus Huanglongbing (HLB)‐associated pathogen ‘Candidatus Liberibacter asiaticus’ (CLas) seriously endangers development of the citrus industry. It spreads via Diaphorina citri in a persistent and propagative manner.RESULTSIn this study, a total of 30 autophagy‐related genes (ATG) were identified in the D. citri genome, among which multiple genes were significantly regulated after CLas infection. Concurrently, CLas infection also leads to an increased number of autophagosomes and enhanced accumulation of ATG8‐II. Ultrastructural observations revealed the presence of bacterial‐like structures within autophagosomes in the midgut of CLas‐infected D. citri. Furthermore, both activation and inhibition of autophagy significantly influenced CLas titers. However, autophagy cannot completely eliminate CLas in D. citri. We identified a CLas effector, SDE4040 (CLIBASIA_04040), that interacts with DcATG8 and co‐localizes on autophagosomes in D. citri. Co‐expression of SDE4040 and DcATG8 induces autophagy in Spodoptera frugiperda (Sf9) cells.CONCLUSIONTaken together, these results indicate that CLas infection activates the autophagy pathway in D. citri, contributing to a reduction in bacterial titer. Our data also revealed that CLas may trigger complex interactions with the insect. © 2025 Society of Chemical Industry.